The present invention relates generally to a sheath used to facilitate percutaneous insertion of devices, such as catheters, into the body and, more specifically, to a sheath which can be torn off after insertion.
The use of catheters to inject, sample, drain, biopsy and implant various instruments in the body has developed into a highly sophisticated area of medical practice. Introduction of catheters into the vascular system without surgical cut down has been practiced for many years under what is termed the Seldinger technique. This technique involves the percutaneous insertion of a catheter through the use of a hollow needle and a wire guide. One modification of this technique, known as the Desilets-Hoffman technique, involves the use of an introducer sheath to permit the percutaneous insertion of a catheter or other instrument not having an open lumen or tapered tip.
In certain situations, such as for example, the transvenous insertion of pacemaker leads into the body, it is not possible to remove the introducer sheath from the inserted instrument unless the sheath is first split longitudinally. As a result, several devices have been developed which disclose a means for splitting the sheath longitudinally after insertion into the body. The most satisfactory one of these devices, and that upon which the present invention is a direct improvement, is disclosed in U.S. Pat. No. 4,306,562 to Osborne. This patent discloses a tear apart cannula made from a flexible material exhibiting the property of longitudinal molecular orientation. The cannula is provided with a pair of longitudinal slits defining tabs at the proximal end of the cannula. While the slits run only a portion of the total length of the cannula, due to the longitudinal molecular orientation construction, the cannula is capable of easily tearing apart so as to permit its removal from any object received therein.
While the Osborne cannula stands as a distinct improvement over other cannulas designed for similar use, there are nevertheless some disadvantages occasioned by its use. One such disadvantage is that the Osborne cannula requires that both hands of the user be employed to manipulate the cannula so as to tear it apart. Further, the Osborne cannula must inherently be split into two for removal, thus creating two pieces of material for disposal. Another disadvantage involves the manner in which the user can temporarily block blood flow or air aspiration when there are no dilators or catheters in the lumen of the introducer cannula. The standard accepted practice used with more conventional introducer cannulas permits the user to block blood flow or air aspiration by placing his thumb over the proximal open end of the cannula and exerting pressure. The Osborne cannula requires the user to squeeze or pinch off the lumen of the sheath at the proximal end. This procedure has encountered some resistance since some physicians fear this damages the cannula and compromises the lumen size. Also in some situations it is desired to use a needle stylet in the sheath so that the sheath can be inserted and advanced into the tissue. Since there is no regular bearing surface at the proximal end of the Osborne cannula, it has been observed that the cannula slits will prematurely tear while it is being inserted and advanced into the tissue with a needle therein. Thus the distance between the needle point and the distal end of the cannula cannot be established and maintained during use.